Adverse effects of microgravity on the magnetotactic bacterium Magnetospirillum magnetotacticum

Bacteria that contain magnetosomes display magnetotaxis and align themselve s to the earth's magnetic held. When magnetotactic bacteria were first isol ated several decades ago it was presumed that geomagnetic orientation allow ed magnetotactic bacteria to orient themselves downward towards sediments w here the habitat is favorable to their growth and metabolism. As more speci es of magnetotactic bacteria have been isolated and studied, differences in magnetotactic responses have been observed which suggested that the primar y role of magnetosomes might simply be to enhance a microorganism's respons e to gravity. To resolve if gravity influences magnetotactic behavior in ba cteria, Magnetospirillum magnetotacticum was used to examine magnetotaxis i n the absence of gravity. Experiments to compare the orientation of bacteri a to north- or south-pole magnets were conducted in normal gravity and in t he microgravity environments aboard the Space Shuttle and Space Station MIR . In each of the microgravity situations studied, bacteria were impaired in their ability to orient to magnets and the failure to exhibit magnetotaxis appeared to be a function of the loss of magnetosomes. The disappearance o f aggregated magnetosomes seemed to correlate with a general loss of cellul ar integrity in microgravity. (C) 2000 Elsevier Science Ltd. All rights res erved.